How to get back to normal animation timeline after using NLA Editor
adding a keyframe, you've started creating an action.

 To get back to "normality" :
open dopesheet


In dopesheet, go to action editor


here you can edit or remove your action


If you're editing an action (hello) animating the same bone(s) as the other one (walk cycle), the action above is the only one that will do something. The action below is "muted" (at least the part that uses the same bone).